For all those saying its ASB there was/is a timeline about the Mongols reaching Central America which was allowed to continue. I'm looking forward to seeing which direction this timeline goes in.
How did they reach Central America?
Anyway, I also think this is ASB, at least in its current format. The best way to do with I think is to A. have better improvements in naval technology. This would require an earlier POD. Say, the Ptolemies get more interested in the sea trade with India for example, and attempt to set up some trade outposts there (not ASB, Roman and Greek sea merchants did frequent the area). So when the Romans come along, there's a budding network and outposts in India, and naval technology is at least slightly improved.
From there have these Jews decide fleeing to these outposts and setting up proper colonies there is the best course of action. Have them maintain some kind of maritime tradition, and over time expand their connections to Indonesia and from there it wouldn't be too hard for them to discover Australia.